An ENGINE or MOTOR is a machine designed to convert one form of
energy into mechanical energy .
Heat engines burn a fuel to create
heat , which is then used to create a force . Electric motors convert
electrical energy into mechanical motion; pneumatic motors use
compressed air and clockwork motors in wind-up toys use elastic energy
. In biological systems, molecular motors , like myosins in muscles ,
use chemical energy to create forces and eventually motion.

The word _engine_ derives from
Old French _engin_, from the Latin
_ingenium_–the root of the word _ingenious_. Pre-industrial weapons
of war, such as catapults , trebuchets and battering rams , were
called _siege engines _, and knowledge of how to construct them was
often treated as a military secret. The word _gin_, as in _cotton gin
_, is short for _engine_. Most mechanical devices invented during the
industrial revolution were described as engines—the steam engine
being a notable example. However, the original steam engines, such as
those by
Thomas Savery , were not mechanical engines but pumps. In
this manner, a fire engine in its original form was merely a water
pump, with the engine being transported to the fire by horses.

In modern usage, the term _engine_ typically describes devices, like
steam engines and internal combustion engines, that burn or otherwise
consume fuel to perform mechanical work by exerting a torque or linear
force (usually in the form of thrust ). Devices converting heat energy
into motion are commonly referred to simply as _engines_. Examples of
engines which exert a torque include the familiar automobile gasoline
and diesel engines, as well as turboshafts . Examples of engines which
produce thrust include turbofans and rockets .

When the internal combustion engine was invented, the term _motor_
was initially used to distinguish it from the steam engine—which was
in wide use at the time, powering locomotives and other vehicles such
as steam rollers . The term _motor_ derives from the
Latin verb _moto_
which means to set in motion, or maintain motion. Thus a motor is a
device that imparts motion.

_Motor_ and _engine_ later came to be used largely interchangeably in
casual discourse. However, technically, the two words have different
meanings. An _engine_ is a device that burns or otherwise consumes
fuel, changing its chemical composition, whereas a motor is a device
driven by electricity , air , or hydraulic pressure, which does not
change the chemical composition of its energy source. However,
rocketry uses the term rocket motor , even though they consume fuel.

A heat engine may also serve as a _prime mover_—a component that
transforms the flow or changes in pressure of a fluid into mechanical
energy . An automobile powered by an internal combustion engine may
make use of various motors and pumps, but ultimately all such devices
derive their power from the engine. Another way of looking at it is
that a motor receives power from an external source, and then converts
it into mechanical energy, while an engine creates power from pressure
(derived directly from the explosive force of combustion or other
chemical reaction, or secondarily from the action of some such force
on other substances such as air, water, or steam).

HISTORY

ANTIQUITY

Simple machines , such as the club and oar (examples of the lever ),
are prehistoric . More complex engines using human power , animal
power , water power , wind power and even steam power date back to
antiquity. Human power was focused by the use of simple engines, such
as the capstan , windlass or treadmill , and with ropes , pulleys ,
and block and tackle arrangements; this power was transmitted usually
with the forces multiplied and the speed reduced . These were used in
cranes and aboard ships in
Ancient Greece , as well as in mines ,
water pumps and siege engines in
Ancient Rome . The writers of those
times, including
Vitruvius ,
Frontinus and
Pliny the Elder , treat
these engines as commonplace, so their invention may be more ancient.
By the 1st century AD, cattle and horses were used in mills , driving
machines similar to those powered by humans in earlier times.

According to
Strabo , a water powered mill was built in Kaberia of
the kingdom of Mithridates during the 1st century BC. Use of water
wheels in mills spread throughout the
Roman Empire over the next few
centuries. Some were quite complex, with aqueducts , dams , and
sluices to maintain and channel the water, along with systems of gears
, or toothed-wheels made of wood and metal to regulate the speed of
rotation. More sophisticated small devices, such as the Antikythera
Mechanism used complex trains of gears and dials to act as calendars
or predict astronomical events. In a poem by
Ausonius in the 4th
century AD, he mentions a stone-cutting saw powered by water. Hero of
Alexandria is credited with many such wind and steam powered machines
in the 1st century AD, including the
Aeolipile and the vending machine
, often these machines were associated with worship, such as animated
altars and automated temple doors.

MEDIEVAL

Medieval Muslim engineers employed gears in mills and water-raising
machines, and used dams as a source of water power to provide
additional power to watermills and water-raising machines. In the
medieval Islamic world , such advances made it possible to mechanize
many industrial tasks previously carried out by manual labour .

In 1206, al-Jazari employed a crank -conrod system for two of his
water-raising machines. A rudimentary steam turbine device was
described by Taqi al-Din in 1551 and by
Giovanni Branca in 1629.

In the 13th century, the solid rocket motor was invented in China.
Driven by gunpowder, this, the simplest form of internal combustion
engine was unable to deliver sustained power, but was useful for
propelling weaponry at high speeds towards enemies in battle and for
fireworks . After invention, this innovation spread throughout Europe.

INDUSTRIAL REVOLUTION

Boulton "> In 1853-57
Eugenio Barsanti and Felice Matteucci
invented and patented an engine using the free-piston principle that
was possibly the first 4-cycle engine.

The invention of an internal combustion engine which was later
commercially successful was made during 1860 by
Etienne Lenoir .

In 1877 the
Otto cycle was capable of giving a far higher power to
weight ratio than steam engines and worked much better for many
transportation applications such as cars and aircraft.

AUTOMOBILES

The first commercially successful automobile, created by
Karl Benz ,
added to the interest in light and powerful engines. The lightweight
petrol internal combustion engine, operating on a four-stroke Otto
cycle, has been the most successful for light automobiles, while the
more efficient
Diesel engine is used for trucks and buses. However, in
recent years, turbo Diesel engines have become increasingly popular,
especially outside of the United States, even for quite small cars.

Horizontally Opposed Pistons

In 1896,
Karl Benz was granted a patent for his design of the first
engine with horizontally opposed pistons. His design created an engine
in which the corresponding pistons move in horizontal cylinders and
reach top dead center simultaneously, thus automatically balancing
each other with respect to their individual momentum. Engines of this
design are often referred to as flat engines because of their shape
and lower profile. They were used in the
Volkswagen Beetle , some
Porsche and Subaru cars, many
BMW and
Honda motorcycles , and aircraft
engines (for propeller driven aircraft).

Advancement

Continuance of the use of the internal combustion engine for
automobiles is partly due to the improvement of engine control systems
(onboard computers providing engine management processes, and
electronically controlled fuel injection). Forced air induction by
turbocharging and supercharging have increased power outputs and
engine efficiencies. Similar changes have been applied to smaller
diesel engines giving them almost the same power characteristics as
petrol engines. This is especially evident with the popularity of
smaller diesel engine propelled cars in Europe. Larger diesel engines
are still often used in trucks and heavy machinery, although they
require special machining not available in most factories. Diesel
engines produce lower hydrocarbon and CO2 emissions, but greater
particulate and
NOx pollution, than gasoline engines. Diesel engines
are also 40% more fuel efficient than comparable gasoline engines.

Increasing Power

In the first half of the 20th century, a trend of increasing engine
power occurred, particularly in the American models. Design changes
incorporated all known methods of raising engine capacity, including
increasing the pressure in the cylinders to improve efficiency,
increasing the size of the engine, and increasing the rate at which
the engine produces work. The higher forces and pressures created by
these changes created engine vibration and size problems that led to
stiffer, more compact engines with V and opposed cylinder layouts
replacing longer straight-line arrangements.

The design principles favoured in Europe, because of economic and
other restraints such as smaller and twistier roads, leant toward
smaller cars and corresponding to the design principles that
concentrated on increasing the combustion efficiency of smaller
engines. This produced more economical engines with earlier
four-cylinder designs rated at 40 horsepower (30 kW) and six-cylinder
designs rated as low as 80 horsepower (60 kW), compared with the large
volume V-8 American engines with power ratings in the range from 250
to 350 hp, some even over 400 hp (190 to 260 kW).

Earlier automobile engine development produced a much larger range of
engines than is in common use today. Engines have ranged from 1- to
16-cylinder designs with corresponding differences in overall size,
weight, engine displacement , and cylinder bores . Four cylinders and
power ratings from 19 to 120 hp (14 to 90 kW) were followed in a
majority of the models. Several three-cylinder, two-stroke-cycle
models were built while most engines had straight or in-line
cylinders. There were several V-type models and horizontally opposed
two- and four-cylinder makes too. Overhead camshafts were frequently
employed. The smaller engines were commonly air-cooled and located at
the rear of the vehicle; compression ratios were relatively low. The
1970s and 1980s saw an increased interest in improved fuel economy ,
which caused a return to smaller V-6 and four-cylinder layouts, with
as many as five valves per cylinder to improve efficiency. The Bugatti
Veyron 16.4 operates with a
W16 engine , meaning that two V8 cylinder
layouts are positioned next to each other to create the W shape
sharing the same crankshaft.

The largest internal combustion engine ever built is the
Wärtsilä-Sulzer RTA96-C , a 14-cylinder, 2-stroke turbocharged
diesel engine that was designed to power the _
Emma Mærsk _, the
largest container ship in the world. This engine weighs 2,300 tons,
and when running at 102 RPM produces 109,000 bhp (80,080 kW) consuming
some 13.7 tons of fuel each hour.

TYPES

An engine can be put into a category according to two criteria: the
form of energy it accepts in order to create motion, and the type of
motion it outputs.

The INTERNAL COMBUSTION ENGINE is an engine in which the combustion
of a fuel (generally, fossil fuel ) occurs with an oxidizer (usually
air) in a combustion chamber . In an internal combustion engine the
expansion of the high temperature and high pressure gases, which are
produced by the combustion, directly applies force to components of
the engine, such as the pistons or turbine blades or a nozzle , and by
moving it over a distance, generates useful mechanical energy .

An EXTERNAL COMBUSTION ENGINE (EC engine) is a heat engine where an
internal working fluid is heated by combustion of an external source,
through the engine wall or a heat exchanger . The fluid then, by
expanding and acting on the mechanism of the engine produces motion
and usable work . The fluid is then cooled, compressed and reused
(closed cycle), or (less commonly) dumped, and cool fluid pulled in
(open cycle air engine).

"
Combustion " refers to burning fuel with an oxidizer , to supply the
heat. Engines of similar (or even identical) configuration and
operation may use a supply of heat from other sources such as nuclear,
solar, geothermal or exothermic reactions not involving combustion;
but are not then strictly classed as external combustion engines, but
as external thermal engines.

The working fluid can be a gas as in a
Stirling engine , or steam as
in a steam engine or an organic liquid such as n-pentane in an Organic
Rankine cycle . The fluid can be of any composition; gas is by far the
most common, although even single-phase liquid is sometimes used. In
the case of the steam engine, the fluid changes phases between liquid
and gas.

AIR-BREATHING COMBUSTION ENGINES are combustion engines that use the
oxygen in atmospheric air to oxidise ('burn') the fuel, rather than
carrying an oxidiser , as in a rocket . Theoretically, this should
result in a better specific impulse than for rocket engines.

A continuous stream of air flows through the air-breathing engine.
This air is compressed, mixed with fuel, ignited and expelled as the
exhaust gas. Examples

The operation of engines typically has a negative impact upon air
quality and ambient sound levels . There has been a growing emphasis
on the pollution producing features of automotive power systems. This
has created new interest in alternate power sources and
internal-combustion engine refinements. Though a few
limited-production battery-powered electric vehicles have appeared,
they have not proved competitive owing to costs and operating
characteristics. In the 21st century the diesel engine has been
increasing in popularity with automobile owners. However, the gasoline
engine and the Diesel engine, with their new emission-control devices
to improve emission performance, have not yet been significantly
challenged. A number of manufacturers have introduced hybrid engines,
mainly involving a small gasoline engine coupled with an electric
motor and with a large battery bank, but these too have yet to make
much of an inroad into the market shares of gasoline and Diesel
engines.

where _r_ is the length of the lever, _F_ is the force applied on it,
and R×F is the vector cross product .
Torque is measured typically
either in newton-metres (N·m, SI units) or in foot-pounds (ft·lb,
imperial units).

POWER

Power is the amount of work being done, or energy being produced, per
unit of time. This is expressed by the formula: P = d W d
t {displaystyle P={frac {mathrm {d} W}{mathrm {d} t}}}

This formula with linear forces and speeds can be used equally well
for both engines outputting thrust and engines exerting torque.

When considering propulsive engines, typically only the raw force of
the core mass flow is considered, leading to such engines having their
'power' rated in any of the units discussed above for forces.

If the engine in question outputs its power on a shaft, then: P
= {displaystyle P=tau omega } .

This is the reason why any engine outputting its power on a rotating
shaft is usually quoted, along with its rated power, the rotational
speed at which that rated power is developed.

Depending on the type of engine employed, different rates of
efficiency are attained.

For heat engines, efficiency cannot be greater than the Carnot
efficiency .

SOUND LEVELS

In the case of sound levels, engine operation is of greatest impact
with respect to mobile sources such as automobiles and trucks. Engine
noise is a particularly large component of mobile source noise for
vehicles operating at lower speeds, where aerodynamic and tire noise
is less significant. Generally speaking, petrol and diesel engines
emit less noise than turboshafts of equivalent power output; electric
motors very often emit less noise than their fossil fuel-powered
equivalents. Thrust-outputting engines, such as turbofans, turbojets
and rockets emit the greatest amount of noise because their method of
producing thrust is directly related to the production of sound.
Various methods have been devised to reduce noise. Petrol and diesel
engines are fitted with mufflers (silencers); newer turbofans often
have outsized fans (the so-called high-bypass technology) in order to
reduce the proportion of noisy, hot exhaust from the integrated
turboshaft in the exhaust stream, and hushkits exist for older,
low-bypass turbofans. No known methods exist for reducing the noise
output of rockets without a corresponding reduction in thrust.